The invention relates to drawing dies having central orifices for working elongated blanks into twist bodies during relative angular movement of the die and the blank as the blank is advanced downstream through the die.
Drawing dies of this type are conventionally defined by spaced planar end surfaces, with the working orifice extending therebetween. The central orifice conventionally necks down from a relatively wide entry area to an interior region of the die, whose cross-section corresponds to the cross-section of the body; in general, such cross-section is non-circular in shape, and varies axially along the body in a spirit of constant radius.
One problem with such conventional dies has been the rapid wearing of the peripheral walls of the central working region of the orifice. In an attempt to compensate for such wear, the areas of the orifice adjacent the interior working region have been modified by the use of irregular profiling, arrived at either by time-consuming calculations or expensive computer-controlled facilities. In addition, such irregular profiling has been found to adversely effect the accuracy of manufacture of the twisted body.